Elsewhere, it was business as usual as the track underwent its makeover for "The Great American Race." The stages for driver introductions and the pre-race concert were already in place, as were the generators on pit road. The Daytona 500 logo was being painted on the grass and other track signage got a touch up. If not for the steady buzz from the welding done on the fence, it would have looked like any other late Saturday night before the 500.

Fans seated in the area of the wreck uploaded videos on YouTube that showed fans fleeing in horror and covering their heads as tires and an engine hurled their way. Most of the videos were soon removed from the video-sharing site.

NASCAR chief marketing officer Steve Phelps said the removal was ordered "out of respect for those injured. Information on the status of those fans was unclear and the decision was made to err on the side of caution with this very serious incident."

The scene was similar to a 2009 race at Talladega Superspeedway - Daytona's sister track in Alabama - when Carl Edwards' car went sailing into the fence on a last-lap accident.

O'Donnell said NASCAR and track officials would continue to strengthen safety standards as needed.

"We'll evaluate the fencing and see if there's anything we can learn from where gates are," he said. "I think we need to take the time to really study it and see what we can improve on, if we can. Certainly, the safety of our fans is first and foremost and we'll make that happen."